Head up displays (HUD) are used to report a message to a user while the user continues to view an outside scene. For example, in an aircraft, the HUD displays important flight parameters to the pilot, on a combiner, without having the pilot to divert his view away from the ground or the aircraft flying nearby, toward the instrument panel or other locations within the cockpit. Methods and systems to construct a HUD are known in the art.
U.S. Pat. No. 7,095,562 B1 issued to Peng et al., and entitled “Advanced Compact Head Up Display”, is directed to a head up display (HUD), utilizing a combiner in the form of a meniscus lens. The HUD includes a liquid crystal display (LCD) image source, and a meniscus combiner. The meniscus combiner includes a pair of meniscus lenses which are bonded together with a suitable cement. The layer between the lenses is used as a holographic mirror.
U.S. Pat. No. 7,068,444 B2 issued to Nishi, and entitled “Image Display Unit and Projection Optical System”, is directed to an optical system for projecting an image on the retina of an eye of a user. The optical system includes an LCD module, a zoom automatic focus control system, a first, second, third and fourth reflection mirror, a relay lens, a diffusion glass, and an eyepiece lens. Light beams from the LCD are reflected by the first mirror, after passing through the zoom automatic focus control system, toward the second reflection mirror. The second reflection mirror reflects the light beams toward the relay lens, which expands the light beams, and transmits the light beams to the third reflection mirror. The third reflection mirror reflects the light beams toward the fourth reflection mirror, which in turn reflects the light beams toward the diffusion glass. The diffusion glass transmits the light beams toward the eyepiece lens, and the eyepiece lens projects the light beams on the retina of the user.
U.S. Pat. No. 6,947,013 B2 issued to D'Achard Van Enschut et al., and entitled “Display Device Combining Ambient Light with Magnified Virtual Images Generated in the Eye Path of the Observer”, is directed to a display device for combining an image generated by an LCD, with the reality image, and displaying the combined image for an observer. The display device includes a light source, a semi-transmissive mirror, an LCD, a magnifying lens, a vertical polarization filter, a horizontal polarization filter, a shutter, and a diminishing lens.
The horizontal polarization filter is located between the light source and the semi-transmissive mirror. The LCD is located between the semi-transmissive mirror and the vertical polarization filter. The magnifying lens is located between the vertical polarization filter and an eye of the observer. The diminishing lens is located on a side of the semi-transmissive mirror, opposite to that of the LCD. The shutter is located between the diminishing lens and the reality image.
Horizontally polarized light is transmitted from the light source toward the semi-transmissive mirror, by the horizontal polarization filter. The horizontally polarized light is reflected by the semi-transmissive mirror toward the LCD, passes through the LCD and is vertically polarized by the vertical polarization filter. The magnifying lens magnifies the image represented by the vertically polarized light, and transmits it toward the eye of the observer. The light from the reality image passes through the shutter and the diminishing lens, toward the semi-transmissive mirror. The semi-transmissive mirror transmits the light from the diminishing lens toward the eye of the observer, thereby allowing the observer to observe the reality image combined with the image generated by the LCD. The diminishing lens compensates for the magnifying effect of the magnifying lens.